0085. MX discovers a dialect's tags from declared folders (target design)

0085. MX discovers a dialect’s tags from declared folders (target design)

Status

Accepted as a target design. Nothing is built. Row: DOM-07.

Date

2026-10-11

Deciders

operator (Saulo Vallory), with MX, 2026-10-11 (the directory name at 09:08). The hook’s design is worked out with MX’s dialect squad, for any dialect and not only Mesh.

Context

Concepts (and later other tags) should be files the user writes, not code in the Mesh repository. MX, as of 2026-10-11:

• lowerSource runs no discovery; the caller passes getCustomTags.
• Only tags/x.tag.ts or tags/x.mx defines a tag.
• A dotted basename such as money.mesh.mx is skipped.
• A tags/ entry silently replaces an mx.contracts tag of the same name.

Decision

• A dialect’s static mx.dialect manifest declares tagDirs (scanned in the usual upward walk; Mesh’s include concepts, and Mesh may add others), optional tagExtensions, whether its tags accept .tag.ts sidecars, and reservedTags.
• Scoping is MX’s usual: per file, the nearest wins.
• A tag’s name is its file name minus the claimed extension: concepts/money.mesh.mx is money.
• Overriding a reserved tag gets a positioned, branded diagnostic, never a throw.
• A generic, synchronous dialect hook turns a tag file into a contract.
• In the user docs, concepts is a folder Mesh loads by itself: concepts are found and loaded automatically, so you do not import them.

Options considered

Mesh scans and passes getCustomTags itself (rejected: every dialect would redo it); an MX feature driven by the manifest (chosen); explicit imports of concept files (ADR-0067’s way, kept for entities).

Trade-off analysis

Discovery in MX serves every dialect and gives the same scoping rules, but it depends on MX work not yet scheduled. The facts above are why Mesh cannot do it alone today.

Consequences

Concepts (ADR-0080) wait for it. No existing record changes. The user docs describe the behaviour only when it is built.

Action items

• MX lead: the manifest keys and the hook (with the MX dialect squad).